A new molecular species of collagen has been isolated from embryonic avian tissues and human cardiovascular tissues. This collagen called type V collagen is comprised of two alpha B and one alpha A chain. Microheterogeneity of the alpha chains within this collagen species have been detected. At present it is not clear whether several different molecular types of collagen are comprised of these two chains such as A3 or B3 but the data obtained to date indicates that this is quite possible. Non-enzymatic hydorxylation of proline and lysine has been successfully accomplished in both free amino acids and in polypeptides. The reaction requires ferrous iron and peroxide, but can also be accomplished with a super-oxide generating system. The identity of the end product as hydroxyproline or hydroxylysine has been confirmed by column chromatographic, high voltage electrophoretic and mass spectrographic analysis. The biological importance of such apparently non-collagenous peptides has yet to be determined. Platelet collagen interaction studies conducted with the five different types of collagen isolated from human tissues indicate that five types IV and V do not effect platelet aggregation or serotonin release. These two collagens, or at least type IV, are present in basement membranes. The basement membrane of the subendothelial space in the vascular tree has not been rigorously characterized, but the data available would indicate that this material is a non-thrombogenic surface. Accordingly vessels denuded of endothelium might not be thrombogenic if the process which removed cells did not remove the underlying basement membrane.